Fix kotlin nullable errors in Input tests

Fix kotlin nullable errors that were exposed by setting the retention
of android.annotation.NonNull and android.annotation.Nullable to
class retention.

Bug: 294110802
Test: builds
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:f3413858f14bf7398453603a8df50a8a9169f6a4)
Merged-In: I35530e7ed63a647c39018ef0ee850ceea4dbc0ba

Change-Id: I35530e7ed63a647c39018ef0ee850ceea4dbc0ba